Antilock control device

ABSTRACT

An antilock control device for the brake assembly of a motor vehicle having the function of detecting ON and OFF signals supplied from a brake lamp switch and representative of the operative and inoperative positions of the brake pedal. When the signal changes from OFF to ON, which means that the brake pedal has been trodden, the antilock control function is disabled so that the pressure generated in the master cylinder will be directly applied to the wheel cylinders. This state continues until the antilock device detects a locking tendency of any wheel. In addition to the brake lamp switch signals, signals representative of the ON and OFF positions of the accelerator pedal may be supplied to the antilock control device so that the antilock control function will be disabled when either the accelerator pedal position signal changes from OFF to ON or the brake pedal position signal changes from ON to OFF.

This application is a continuation of allowed application Ser. No.07/310,830, filed Feb. 8, 1989 now U.S. Pat. No. 5,102,204.

BACKGROUND OF THE INVENTION

The present invention relates to an antilock control device forefficiently operating the braking system of a motor vehicle even in caseof a cadence brake.

An antilock brake control device is designed to detect the lockingtendency of any wheel and reduce the hydraulic pressure in the brakewheel cylinder for the locking wheel to a lower level than the hydraulicpressure in a master cylinder controlled by the driver, therebypreventing the wheel from locking.

After the wheel has cleared out of the locking tendency, it is nownecessary to increase the hydraulic pressure in the wheel cylinderbecause otherwise the braking force would be insufficient. But if thehydraulic pressure in the master cylinder is applied to the wheelcylinder too quickly, the wheel may soon fall into a locking stateagain. Thus, it is necessary to increase the hydraulic pressure in thewheel cylinders not sharply but gradually. For this purpose, it wasproposed to provide the hydraulic circuit with two functions, i.e. thefunction of holding the pressure in the wheel cylinders and the functionof bringing the wheel cylinders into direct communication with themaster cylinder to increase the pressure in the wheel cylinders. Withthis arrangement, the hydraulic pressure in the wheel cylinders can beincreased gradually while repeating the pressure increase and thepressure hold. For the same purpose, it was also proposed to provide athrottle valve or a flow control valve in the hydraulic circuit toselectively repeat a sharp pressure increase and a moderate pressureincrease.

When the automobile is running on a rough surface, some of its wheelsmight be judged from the signals from the wheel speed sensors as if theyare falling into a locking state in spite of the fact that the brakepedal is not operated, thus causing the antilock device to give apressure reduction command. Even after the automobile has passed therough surface and the wheels have been judged to be recovering from thelocking state, the wheel cylinders are kept not in direct communicationwith the master cylinder as discussed above. If the brake pedal istrodden in such a situation, the hydraulic pressure generated in themaster cylinder will not be transmitted to the wheel cylinders directlyand smoothly, thus delaying the braking effect.

As one solution to this problem is to provide means for judging whetherthe brake pedal is in its operative or inoperative position by checkinge.g. signals representative of the ON or OFF position of a stop lampswitch to keep the antilock device inoperative, i.e. keep the mastercylinder in communication with the wheel cylinders as long as the brakepedal is in its inoperative position. This will allow the hydraulicpressure in the wheel cylinders to reach the pressure level in themaster cylinder as soon as possible. But this solution has one drawbackthat the signals representative of the operative and inoperativepositions of the brake pedal are not necessarily reliable. For example,the signal may remain OFF even if the brake pedal is actually put intoits operative position, or it may remain ON even if the brake pedal isnot trodden owing to the fusing of the switch.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an antilock controldevice which operates normally even if a brake pedal position detectoris out of order and which will not cause a delay in the braking actionas far as the detector is working normally.

When an antilock device finds that a wheel is recovering from a lockingstate, it will give either a combination of brake pressure increase andhold commands or a combination of sharp and moderate brake pressureincrease commands. The hydraulic circuit is controlled exactly inconformity with these commands. Thus, even if the brake pedal is troddenin this state, the hydraulic pressure generated in the master cylinderby operating the brake pedal would not be directly applied to the wheelcylinders. According to the present invention, the hydraulic pressure inthe master cylinder will be directly applied to the wheel cylinders,when either the brake pedal position detector detects a change of signalfrom OFF to ON or the accelerator pedal position detector detects achange of signal from ON to OFF.

According to the present invention, the brake pedal position signals aresupplied to the antilock control device. This will allow the brakes tobe applied reliably by treading of the brake pedal even while theantilock control is working e.g. due to the fact that the automobile isrunning on a rough surface. Even if the brake pedal position detectorshould get out of order, the antilock control device will operatenormally, thus ensuring a safe drive.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and objects of the present invention will become apparentfrom the following description taken with reference to the accompanyingdrawings, in which:

FIG. 1 is an electric circuit diagram of the antilock control deviceaccording to the present invention;

FIG. 2 is a block diagram of the electronic control unit of the same;

FIG. 3 is a schematic diagram showing how the electronic control unit isrelated to the hydraulic circuit of the same;

FIG. 4 is a flow chart of the program in the phase selection controlunit shown in FIG. 3; and

FIG. 5 is a graph showing how the pressure changes by alternatelyincreasing and reducing the fluid pressure.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, the antilock control device according to thepresent invention has an electronic control unit (hereinafter referredto as ECU) which executes various operations and judgements on the basisof the signals from wheel speed sensors S1-S4 to actuate solenoidsSOL1-SOL6 in pressure control valves (not shown) for wheel cylinders foractuating wheel brakes and open and close a relay ML for a motor M fordriving a pump P in a hydraulic unit (not shown), thereby increasing,holding and reducing the hydraulic pressure in the wheel cylinder foreach wheel brake.

The ECU has a monitoring circuit which turns on a warning lamp w when itdetects any abnormal state, and simultaneously opens a failsafe relay FLto disable the antilock control, thus allowing manual brake control.

The ON-OFF signals from a brake switch SW for stop lamp STP are appliedto the ECU. The ON-OFF signals are processed as brake pedal positionsignals as will be described in detail later. Similarly, signals from anaccelerator switch SW are also supplied to the ECU.

The mark "+B" means that the line is connected to a power source and"IG", does that it is connected to an ignition switch.

The function of the ECU is schematically shown in FIG. 2. The signalsfrom the wheel speed sensors S1 to S4, which are AC voltage signals, areconverted into pulses in an interface circuit and given to a pulseprocessing circuit where the pulses are counted. A CPU then computes andanalyzes the pulse counts according to its program and, on the basis ofthe results of computing gives commands to a solenoid actuating circuitand a motor relay actuating circuit to actuate the solenoids SOL1 toSOL6 for the pressure control valves and the motor relay ML,respectively.

The ON-OFF signals from the brake switch SW for the stop lamps and theaccelerator pedal switch are binary-coded in an interface circuit andapplied to the CPU so as to be processed according to its program.

More specifically, as shown in FIG. 3, the signals from the wheel speedsensors S1 are converted into wheel speed signals in a wheel speeddetector including an interface circuit and a pulse processing circuitand are applied to a processing/lock state detecting means, whichcalculates the deceleration, estimated vehicle speed and so forth on thebasis of the wheel speed signals to detect any locking tendency of thewheel. If it is judged that the wheel is locking or about to lock, fromthe fact that the deceleration has fallen below a predetermined value orthe slip speed (which is the difference between the estimated vehiclespeed and the wheel speed) has exceeded a predetermined value, the lockstate detecting means commands the solenoid actuating circuit to reducethe hydraulic pressure. In response to this command, the solenoidactuating circuit will energize the solenoids SOL1 and SOL2 to move apressure control valve 21 to the lefthand side of FIG. 3 and a pressurecontrol valve 22 upward. This will cause the hydraulic circuit for awheel cylinder 24 to be cut off from a hydraulic pressure sourcecomprising a master cylinder 23 and an accumulator 26 and bring thehydraulic circuit for the wheel cylinder 24 into communication with thatfor a reservoir 25. A pump P will then drain the brake fluid in thereservoir 25 back into the accumulator 26 and the master cylinder 24,thus lowering the braking pressure in the wheel cylinder 24.

The wheel speed thus begins to increase. When the deceleration or theslip speed rises above a predetermined value, the lock state detectorjudges that the wheel has cleared out of the locking tendency andcommands the solenoid actuating circuit to increase pressure. Thecircuit then deenergizes the solenoids SOL1 and SOL2 to allow thepressure control valves 21 and 22 to return to their original positionsshown in FIG. 3. Now the hydraulic circuit of the wheel cylinder 24 arebrought into communication with the hydraulic pressure source again,thus increasing the brake pressure in the wheel cylinder.

If a pressure hold command has to be given while a pressure increase orpressure reduction command is being given, the solenoid SOL1 may beenergized and the solenoid SOL2 be deenergized to move the pressurecontrol valve 21 to the lefthand side of FIG. 3 while keeping thepressure control valve 22 in the position of FIG. 3. In this state, thehydraulic circuit of the wheel cylinder 24 is cut off from both thepressure source and the reservoir 25, so that the brake pressure will bekept constant.

The conditions and timing of giving a pressure hold command while apressure reduction command is being given may be determined atdiscretion. For example, a pressure hold command may be given when theduration of the pressure reduction command has reached a predeterminedpoint or when the wheel deceleration has exceeded a threshold value.

Similarly, the conditions and timing of alternately giving the pressureincrease command and the pressure reduction command may be determined inany suitable manner. Ordinarily, pressure hold commands are given atequal time intervals by use of e.g. a pulse generator.

The device shown in FIGS. 1 and 2 is a 3-channel control device withthree pairs of solenoids, one for the front right wheel, one for thefront left wheel and one for both rear wheels. The four wheels may becontrolled individually by means of a 4-channel control device.

Other indices than the deceleration or slip speed may be used to judgewhether the wheels are on the way to lock or recovering from lockingstate.

The signals from the brake switch SW are converted into ON-OFF signalsrepresentative of the ON and OFF positions of the stop lamp switch inthe detector means including the interface circuit and those of theaccelerator are fed to a phase selection switch control unit forselecting a processing phase. The ON-OFF signals are then processedlogically to control the processing/lock state detecting means.

The ON-OFF signals are processed in the order of the flow chart of FIG.4. The antilock control according to the present invention includesthree phases, i.e. Phase I wherein a pressure increase command isnormally given, Phase II wherein pressure reduction and pressure holdcommands are alternately given, and Phase III wherein pressure increaseand pressure hold commands are alternately given.

The routine of FIG. 4 starts at Step 1 wherein the program isinitialized and set to Phase I. In Step 2, logical operations areexecuted to calculate the wheel speed, estimated vehicle speed, wheeldeceleration and slip speed to judge whether or not the wheels are inthe lock state. The program then proceeds to Step 11 where it is judgedwhether the accelerator switch has been turned OFF. If it is so judged,to program proceeds to Step 6 and enters into Phase I to keep a pressureincrease command. If it is judged no, the program then proceeds to Step3 wherein it is judged whether the signals from a brake pedal positiondetector has changed from OFF to ON. If so judged, the program proceedsto Step 6 and enters into Phase I to keep a pressure increase command.

If judged "No" in Step 3, it is checked in Step 4 in which phase theprogram is. The program proceeds to Step 5 because the phase has beenset to I in Step I. In Step 5, it is judged whether or not the wheel isfalling into lock, on the basis of the values obtained as a result ofthe operations in Step 2. The wheel may be judged to be falling intolock when the slip speed and/or the wheel deceleration has exceeded athreshold value.

If judged No, the program proceeds to Step 6 to enter into Phase I.

If judged Yes in Step 5, the program proceeds to Step 8 to enter intoPhase II wherein pressure reduction or pressure hold command is issued.In this phase, the pressure reduction command is basically given and thepressure hold command may be issued when the duration of the pressurereduction command has reached a predetermined point or when the wheeldeceleration has exceeded a predetermined threshold value.

If it is judged in Step 4 that the current phase is at phase II, it isjudged in Step 7 whether or not the wheels are recovering from lockingstate. This judgement may be made e.g. by checking whether or not theslip speed or the wheel deceleration or acceleration has exceeded apredetermined threshold value.

If judged No, the program proceeds to Step 8 because the wheels have notrecovered from the locking state. If judged Yes in Step 7, the programproceeds to Step 10 to enter into Phase III and thus issue the pressureincrease and pressure hold commands alternately. A pulse generator maybe employed to allow these two commands to be changed over from one tothe other at fixed time intervals.

The program then returns to Steps 2 and 3 from Step 10. If it is judgedin Step 3 that the position of the switch SW remains unchanged, becausethe program is now in Phase 3, it proceeds through Step 4 to Step 9where the number of issuing of pressure increase and pressure holdcommands in Step 10 is counted. If it is over a preset value, theprogram proceeds to Step 6. If not, the program proceeds to Step 10 andreturns to Step 2.

In Phase III, a sharp pressure increase command and a moderate pressureincrease command may be alternately given instead of a combination ofpressure increase and pressure hold commands. The gradient of pressureincrease may be controlled by means of a flow control valve or by use ofa pulse duration modulation method in which the ratio of the duration ofeach pressure increase to that of each pressure reduction is adjusted.The braking pressure can be held constant by making equal the widths ordurations of pressure increase and pressure reduction pulses to eachother.

In the preferred embodiment, a pressure increase keeping command isgiven when the ECU detects a signal change from OFF to ON position ofthe stop lamp switch, i.e. that the brake pedal is now set in itsoperative position. In addition to such brake pedal position signals,signals representative of the position of the accelerator pedal may beused. In this arrangement, a pressure increase keeping command will beissued if the ECU detects either a signal change representative of theoperative position of the brake pedal from its inoperative position or asignal change representative of the inoperative position of theaccelerator pedal from its operative position. This ensures a reliablebrake control even if the brake pedal switch breaks down. Anotheradvantage of this arrangement is that since the accelerator pedal isusually released to its inoperative position before operating the brakepedal, a pressure increase command can be issued more quickly than whenusing only the brake pedal position signals, thus improving theresponsiveness of control. Practically no problem will be encounteredeven if a pressure increase keeping command is issued when theaccelerator pedal is released.

What is claimed is:
 1. An antilock control device, comprising:a wheelspeed detecting means; a processing/lock state detecting means forexecuting logical operations on the basis of wheel speed signalssupplied from said wheel speed detecting means and for effectingantilock control by issuing commands to reduce, hold or increase a brakepressure in accordance with the executed logical operations; a solenoidactuating means for actuating solenoids for pressure control valves inbrake pressure circuits in response to said commands to reduce, hold orincrease a brake pressure from said processing/lock state detectingmeans when said processing/lock state detecting means is activated toeffect the antilock control; a brake pedal position detecting means fordetecting whether a brake pedal is in its operative ON or inoperativeOFF position; and a control means for controlling the brake pressureaccording to the antilock control effected by said processing/lock statedetecting means when said processing/lock state detecting means isactivated to effect the antilock control and for otherwise bringing saidbrake pressure up to a hydraulic pressure of a master cylinder asquickly as possible, initializing means initially deactivating theantilock control of said processing/lock state detecting means when saidbrake pedal position detecting means detects that the brake pedal haschanged from the inoperative OFF position to the operative ON positionand said control means subsequently reactivating the antilock control ofsaid processing/lock state detecting means when the logical operationsexecuted by said processing/lock state detecting means indicate alocking tendency of a respective wheel.
 2. An antilock control devicecomprising:a wheel speed detecting means; a processing/lock statedetecting means for executing logical operations on the basis of wheelspeed signals supplied from said wheel speed detecting means and foreffecting antilock control by selectively issuing commands to reduce,hold or increase a brake pressure in accordance with the executedlogical operations; a solenoid actuating means for actuating solenoidsfor pressure control valves in brake pressure circuits in response tosaid commands to reduce, hold or increase a brake pressure from saidprocessing/lock state detecting means when said processing/lock statedetecting means is activated to effect the antilock control; a brakepedal position detecting means for detecting whether a brake pedal is inits operative ON or inoperative OFF position; and a control meansoperatively connected to said brake pedal position detecting means andfor activating the antilock control of said processing/lock statedetecting means while the brake pedal is in its inoperative OFFposition, and initializing means for initially deactivating the antilockcontrol of said processing/lock state detecting means when said brakepedal position detecting means detects that said brake pedal has changedfrom its inoperative OFF position to its operative ON position and saidcontrol means subsequently reactivating the antilock control of saidprocessing/lock state detecting means when the executed logic operationsof said processing/lock state detecting means indicate a lockingtendency of a respective wheel.